A semiconductor chip, or die (such as an image sensor chip) is fabricated on a single semiconductor wafer, along with hundreds and in some cases thousands of copies of the same die. The cutting to separate a semiconductor wafer into individual dies can be done with a die saw (such as a diamond saw). Cuts are made along areas of non-functional semiconductor material separating each die known as scribe lines. Using a diamond saw introduces mechanical stress to the semiconductor wafer and can result in cracking at the die edge and compromising the integrity and reliability of the integrated circuit. One structure used to make a die less susceptible to the mechanical stress of die saws are seal rings. A seal ring in a die is formed in or on an outer region of one or more dielectric layers of a semiconductor substrate to protect the integrated circuit from contaminants (e.g. sodium) and make a die less susceptible to the mechanical stress caused by the die saw.
Many semiconductor imaging sensors today are front side illuminated. That is, they include imaging arrays that are fabricated on the front side of a semiconductor wafer, where light is received at the imaging array from the same front side. However, front side illuminated imaging sensors have many drawbacks, one of which is a limited fill factor.
Backside illuminated imaging sensors are an alternative to front side illuminated imaging sensors that address the fill factor problems associated with front side illumination. Backside illuminated imaging sensors include imaging arrays that are fabricated on the front surface of the semiconductor wafer, but receive light through a back surface of the wafer. Color filters and micro-lenses may be included on the back surface of the wafer in order to improve the sensitivity of the backside illuminated sensor. However, to detect light from the backside, the wafer must be extremely thin. The thickness of the wafer may also be reduced in order to improve the sensitivity. However, the thinner the wafer, the more susceptible it becomes to physical damage during the various manufacturing stages. That is, as the semiconductor wafer is thinned, the weaker it becomes, making the backside illuminated imaging sensor wafer even more susceptible to the mechanical stress of die saws.